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Re: Semantics, in particular DAML+OIL semantics

From: Bob MacGregor <macgregor@ISI.EDU>
Date: Mon, 12 Aug 2002 10:57:05 -0700
Message-ID: <00a501c2422a$68470660$f8800980@STRIKER>
To: "Ian Horrocks" <horrocks@cs.man.ac.uk>, <www-rdf-logic@w3.org>

From: "Ian Horrocks" <horrocks@cs.man.ac.uk>
To: <www-rdf-logic@w3.org>
Sent: Monday, August 12, 2002 03:51
Subject: Semantics, in particular DAML+OIL semantics
> ...
> For example, when we parse an OWL ontology we may find that instead of
> using the familiar subClassOf property, it contains lots of statements
> like "Person foo Animal". If we allow statements in the ontology to
> constrain the meaning of the syntax, then we may be able do deduce
> that foo is equivalent to subClassOf, and that this is therefore a
> meaningful OWL statement. The reasoning required for this deduction
> may be extremely complex. It may even be IMPOSSIBLE to be sure that we
> have derived the complete syntactic meaning of an OWL ontology
> (because the language is undecidable).
> 
> Another example. In OWL, transitive properties cannot be used in
> cardinality restrictions. If we allow inference to be used to deduce
> that a property is a transitive property, then when we parse an OWL
> ontology we can't be sure that it is valid until we have checked that
> none of the properties used in cardinality constraints can be deduced
> to be transitive. Again, the required reasoning may be very complex,

So you seem to be saying that OWL can't allow assertions about
classes and properties (like "Person foo Animal") except for a few 
built-in predicates, and this is because there is a messy interaction
with the 'transitive' property.  

My guess is that the utility of second-order
assertions/statements exceeds the utility of the 'transitive' property by a couple
orders of magnitude.   That RDF allows second-order statements is
one of its cardinal virtues.  On the other hand, I work with rule-based
systems (instead of DL systems), and in all cases transitivity appears as an
*emergent* property (derivable from the rules) rather than something
that is explicitly asserted.  The appearance here is that we are catering to
a marginal set of applications, and ruling out large classes of useful
ones.  

If indeed HOW syntax and certain OWL properties (like transitivity) are
incompatible from a practical/simplicity standpoint, it would be preferable to drop those
properties and to keep the second-order assertions.  I would be interested to know
which properties we would need to toss out in order to achieve this effect.

Regards, Bob
Received on Monday, 12 August 2002 14:00:43 UTC

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